Nasa rules out Baptistina asteroid in dinosaur kill-off

An infrared Nasa space telescope has provided key evidence that
an asteroid candidate for the mass extinction of the dinosaurs has
been wrongly accused and was not
to blame.

Most scientists agree that a huge asteroid collided with the
Earth some 65 million years ago, ending the era of the dinosaurs
through a catastrophic global cull. The identity of the meteorite
is unknown, but a 2007
visible-light study suggested (PDF) that the remnants of an
asteroid called Baptistina was a possible suspect.

The hypothesis says that Baptistina crashed into another
asteroid in the belt between Mars and Jupiter 160 million years
ago, which sent shattered segments the size of mountains flying
into the solar system. One of those hit Earth and killed off the dinosaurs.

Now, however, new evidence from the Wide-field Infrared Survey Explorer (WISE) has ruled out
Baptistina entirely. "As a result of the WISE science team's
investigation, the demise of the dinosaurs remains in the cold case
files," said Nasa's Near Earth Object (NEO) program executive
Lindley Johnson.

The discrepancy is in the technique used to gauge the asteroid's
real age. If you take family members of Baptistina, work out their
size and reflectivity you can calculate how much time was required
for those chunks to reach their current locations. Under visible
light that estimate was 160 million years old. Under WISE's far
more accurate infrared, Baptistina is just 80 million years
old.

"This doesn't give the remnants from the collision very much
time to move into a resonance spot, and get flung down to Earth 65
million years ago," said NEOWISE's Amy Mainzer, a co-author of the
study. Resonance spots are areas in the asteroid belt where the
gravity of nearby planets can send asteroids flying off into space.
"This normally takes many tens of millions of years," explains
Mainzer.

While Baptistina has been cleared of all charges, the NEOWISE
data captured from January 2010 to February 2011 will help to
disentangle asteroid families that overlap and trace their
histories. "We are working on creating an asteroid family
tree of sorts," said Joseph Masiero, the lead author of the
study.

Whatever did in the dinosaurs, Yale
paleontologists argue that the same asteroid killed off
primitive, Cretaceous-era, birds in the same go. A study led by
Yale researcher Nicholas Longrich looked at about two dozen bird
fossils discovered in North America and found that many different
bird species died out 65 million years ago, too.

"There's been growing evidence that these birds were wiped out
at the same time as the dinosaurs," Longrich said. "But this new
evidence effectively closes the book on the debate."